1. Field of the Invention
The present invention relates to modified polyolefins with an exceptional profile of properties, the preparation of which is based on semicrystalline polyolefins with isotactic structural elements, to a process for preparation thereof and to the use thereof, especially as an adhesive or as a constituent of adhesives.
2. Description of the Related Art
Amorphous poly-alpha-olefins serve in many cases as adhesive raw materials for a wide range of applications. The field of use extends from the hygiene sector through laminations and packaging adhesives as far as construction adhesives and uses in wood processing. Unmodified amorphous poly-alpha-olefins (known as APAOs) are notable for purely physical curing, which is reversible as desired owing to the thermoplastic character thereof. However, they have only limited tensile strengths and adhesive shear strengths, and a relatively low thermal stability. Moreover, they cannot be used to achieve covalent incorporation of reactive surface groups (for example —OH) into an adhesive bond.
The described disadvantages of unmodified APAOs can be remedied by a subsequent functionalization (modification), for which carboxylic acids or carboxylic acid derivatives and/or silanes in particular can be used for modification.
The preparation of silane-modified polyolefins by reaction of polyethylene with unsaturated silanes has been known for sometime. EP 0004034 gives an early description of a method for crosslinking poly(α-olefins) with the aid of silane bonds, the intention being to achieve maximum degrees of crosslinking. The crosslinking directly follows the grafting and leads to stiff, high-strength materials with low embrittlement temperature, as used, for example, for the production of cable sheathing and/or mouldings. The polymers described cannot be used as adhesives.
DE 1963571, DE 2353783 and DE 2406844 describe processes for crosslinking polyethylene polymers or ethylene copolymers which contain small amounts of propene and/or 1-butene. The target products are crosslinked mouldings based on polyethylene.
DE 2554525 and DE 2642927 describe processes for producing extruded products, including the silane functionalization of a polymer, the incorporation of a silanol condensation catalyst, and the shaping and crosslinking of the polymer, in one operation, by using an extruder. The end applications mentioned are cables, pipes and hoses. Adhesive bonds are not possible with the polymers produced in this way, and further processing overall is possible only to a very limited degree owing to the crosslinking performed immediately after the modification.
It has likewise been known for sometime that it is possible to improve the adhesion of polyolefins to functional surfaces, for example glass, by the introduction of silane groups. For instance, U.S. Pat. No. 3,075,948 gives an early description of graft polymers consisting of unsaturated silane monomers and solid poly(alpha-olefins) having 2-6 carbon atoms, which are said to have improved heat resistance and good adhesion to glass. The resulting modified polymers are used for the production of mouldings and containers, and as a coating for glass vessels; they are not suitable for use as melt-applied adhesives owing to the completely different profile of requirements (melt viscosity, material stiffness in the uncrosslinked state, etc.).
The use of amorphous poly(alpha-olefins) for silane crosslinking is also already known. For example, EP 0260103 describes amorphous silane-modified polymers with a saturated carbon skeleton and low molecular weight, which are used as coating materials for protection from weathering influences. Examples of such polymers include copolymers of ethylene and/or α-olefins, especially EPM and EPDM. The base polymers described are amorphous and rubber-like, and have a high elasticity. Owing to their rubber-like character, processability in the uncrosslinked state is poor. The products are unsuitable for the intended applications in the adhesives and sealants sector in the present application.
DE 4000695 describes the use of substantially amorphous poly(alpha-olefins) in a process in which the APAOs are reacted with a free-radical donor and optionally additionally graftable monomers (e.g. vinylsilanes) under simultaneous shear stress. The resulting products are suitable for use as carpet coating materials or as melt-applied adhesives. The substantially amorphous polyolefins used to prepare the modified poly(alpha-olefins), however, themselves (i.e. in the unmodified state) have only poor to moderate material or adhesive properties, more particularly only low adhesive shear strengths on untreated isotactic polypropylene and only low tensile strengths, such that the modified polymers are also suitable only for applications with low requirements. More particularly, the unmodified, predominantly amorphous polyolefins have a high polydispersity, which leads to disadvantages in material cohesion, and to problems with outgassing low molecular weight constituents. The microstructure of the polymer chains is also not very well-defined, one reason being the heterogeneous polymerization catalysts used to prepare the unmodified polyolefins, and so controlled adjustment to particular material or adhesive requirements is possible only with difficulty. An additional factor is that the modified polymers possess only low functionalization, since the ratio of graft polymerization to chain cleavage is unfavourable. Owing to the low functionalization, the crosslinking reaction proceeds slowly; attachment to reactive surfaces is only relatively weak. An additional factor is that the tensile strength both of the uncrosslinked and of the crosslinked modified polyolefin reaches only relatively low values, as a result of which the products remain excluded from many areas of application.
In JP 2003-002930, graft polymers are prepared from amorphous poly(α-olefin)s, unsaturated carboxylic acids and optionally additionally unsaturated aromatic substances (e.g. styrene). The polyolefins used are amorphous and do not have a crystallinity of >1 J/g in DSC measurements. Moisture-crosslinking monomer systems, for example vinylsilanes, are not discussed; the grafted polyolefins do not have the desired material parameters owing to the properties of the base polymer thereof and the graft monomers used; more particularly, they are too soft, have only a low heat resistance and exhibit too low a tensile strength.
WO 03/070786 describes a process for preparing modified poly(1-butene) polymers, the modified poly(1-butene) polymers obtainable therefrom, and an adhesive composition comprising the modified poly(1-butene) polymers. The poly(1-butene) base polymer used for the modification has a melting point in the range from 0 to 100° C., an isotacticity index of <20% and a polydispersity of <4.0. The graft monomers mentioned are unsaturated carboxylic acids, carboxylic anhydrides, or corresponding derivatives such as amides, esters, etc.
Moisture-crosslinking monomers, for example vinylsilanes, are not described. The modified polymers prepared are relatively soft and of relatively waxy nature owing to their low crystallinity. The low melting point causes poor heat resistance of the adhesive bonds. The polymers are unsuitable for the applications intended in the present application.
WO 2006/069205 describes modified polyolefins with low metal contents based on low-viscosity polypropylene polymers with a propylene content of >50 mol % and a proportion of isotactic propylene triads of >85%, which can be prepared, among other methods, by a free-radical graft polymerization. The described metal contents of <50 ppm can only be achieved via the use of complex “non-metallocene” catalysts together with aluminium-free cocatalysts (e.g. borate cocatalysts), which lead to numerous disadvantages. Polymers with high solubility both in xylene and in tetrahydrofuran at room temperature, which contain only a very low content of low molecular weight species (<1000 daltons) and nevertheless have a high enthalpy of fusion, are not obtained in this way. Owing to the material properties of the base polymers used, the products obtained are unsuitable for the fields of use intended in the present application.
WO 2007/067243 describes polypropylene polymers functionalized by carboxylic acids and having a high to very high propylene content (75-90 mol %), which are prepared on the basis of propylene-based homo- and/or copolymers with a weight-average molar mass of <100 000 g/mol, a melting point of <157° C. and a melt viscosity at 190° C. of <40 000 cPs at reaction temperatures of 130-165° C. Moisture-crosslinking systems, for example based on silanes, are not described. Owing to the base polymers used and the graft monomers used, the products described are unsuitable for the fields of use intended in the present application.
WO 91/06580 describes silane-modified unsaturated amorphous polymers which can be used in the crosslinked state, for example as mouldings. Further use examples of the silane-modified polymers include adhesive compositions, including melt-applied adhesives. Examples of unsaturated base polymers include rubber-like polymers, for example styrene-butadiene block copolymers (SBS), styrene-isoprene block copolymers (SIS), styrene-butadiene rubber (SBR), nitrile rubber, polychloroprene rubber and butyl rubber. All base polymers mentioned have rubber elasticity (i.e. also poor processability) and/or other adverse material properties (for example poor heat resistances), which make them unsuitable for melt-applied adhesive applications.
The use of silane-modified polymers in hotmelt adhesives is likewise known. For example, WO 89/11513 describes an adhesive composition which contains at least one silane-modified or silane-grafted semicrystalline polymer. The base polymers mentioned are especially homo-, co- and terpolymers of C2-6-α-olefins, and also isotactic polypropylene polymers and blends of polypropylenes, especially when they also contain atactic polypropylene. The graft reaction proceeds at temperatures of 140 to 250° C. Atactic polypropylene without defined polymer microstructure intrinsically has a very low softening point [see, for example: H.-G. Elias; Makromoleküle [Macromolecules]; Vol. III; Wiley-VCH: Weinheim; 2001]. The procedure described in WO 89/11513 leads to products with unsatisfactory material properties, especially with regard to cohesion, adhesion (adhesive shear strength) and heat resistance in the uncrosslinked state (for example immediately after application). The adjustment of the viscosity, melting behaviour and tack of the adhesive composition is attributed causally to the use of relatively long-chain silane monomers (≧3 connecting atoms between silicon atom and the polymer chain), which are said to lead to a “more open structure”. The use of relatively long-chain silane monomers is disadvantageous in that it leads to weaker crosslinking as a result of a higher degree of polymerization of the network chains (i.e. of the monomeric base units between two crosslinking sites), which additionally has an adverse effect on the material properties of the graft polymer.
DE 19516457 describes a crosslinkable adhesive composition consisting of at least 50% by mass of a silane-grafted polyolefin and additionally of a carboxylic acid-grafted polyolefin. The base polymers specified for the grafting are poly(ethylene-co-vinyl acetate), polypropylene, polyethylene, poly(ethylene-co-methacrylate) and poly(ethylene-co-methacrylic acid). Owing to the base polymers used and the graft monomers used, the products described are unsuitable for the desired fields of use.
EP 1508579 describes (silane-)modified crystalline polyolefin waxes with a high propylene content. Owing to their wax-like properties and the resulting poor adhesive properties, the polymers described are unsuitable for the fields of use intended. High functionalization according to the present requirements is not achievable owing to the material properties of the base polymers used.
WO 2007/001694 describes adhesive compositions which contain functionalized polymers (preferably maleic anhydride-grafted propylene polymers). The base polymers used are propylene(co)polymers with high isotactic contents and a polydispersity of 1.5 to 40, i.e. predominantly crystalline polymers which possess a very broad molar mass distribution, as normally achievable only in polymers with multimodal distribution. The weight-average molar mass of the polymers used with preference is up to 5 000 000 g/mol, i.e. predominantly in the range of very high molar masses or melt viscosity, which is likewise expressed by the specified limit for the melt index of 0.2 g/10 min. Polymers with a very broad molar mass distribution, especially with a molar mass distribution of >4, however, in free-radically initiated graft reactions, exhibit a very inhomogeneous distribution of functional groups on the polymer chains. More particularly, the grafted polymers contain very high proportions of short chains without a functional group or with only one or a maximum of two functional groups, which either do not enable any reactive connection at all (no functional group), or else are not capable of forming three-dimensional networks. This in turn leads both to poor adhesion and to relatively poor cohesion. Polymers with very high molar masses and very high melt viscosity are additionally difficult to process especially in melt processes, and, owing to the great viscosity difference, have a poor miscibility with monomers and free-radical initiators, which leads to inhomogeneous products with a poor profile of properties.
WO 2007/002177 describes adhesive compositions based on poly(propylene) random copolymers, functionalized polyolefin copolymers which are rich in syndiotactic units, and non-functionalized adhesive resins, the poly(propylene) random copolymers having an enthalpy of fusion of 0.5 to 70 J/g and a proportion of isotactic propylene triads of at least 75% (more preferably >90%), and the functionalized (syndiotactic) polymers used having a content of functional monomer units of at least 0.1% and being present with a proportion of <5% by mass in the adhesive composition. The poly(propylene) random copolymers described have a polydispersity of 1.5 to 40, which indicates a multimodal molar mass distribution and the simultaneous presence of a plurality of catalyst species. The specified melting range of 25 to 105° C., which has several melting peaks of different intensity, points in the same direction, the specified limit of 105° C. having a low value unusual for polypropylene polymers, especially for isotactic polypropylene polymers. Polymers with a very broad molar mass distribution, especially with a molar mass distribution of >5, exhibit a very inhomogeneous distribution of functional groups on the polymer chains in free-radically initiated graft reactions. More particularly, the grafted polymers contain very high proportions of short chains without a functional group or with only one or a maximum of two functional groups, which either do not enable any reactive connection at all (no functional group), or else are not capable of forming three-dimensional networks. This in turn leads both to poor adhesion and to relatively poor cohesion. The specified upper limit for the melting range ensures a low thermal stability of the corresponding bonds.
WO 2007/008765 describes the use of low-viscosity silane-grafted poly(ethylene-co-1-olefin) polymers as an adhesive raw material. The polymers used for modification have an ethylene content of at least 50 mol % of ethylene. The 1-olefin comonomers include numerous higher 1-olefins, for example 1-hexene and 1-octene, but also some branched 1-olefins, for example 3-methyl-1-pentene and various other monomers, for example dienes, styrene, etc., which do not meet the above “1-olefin” requirement, and therefore lead to polymers with completely different material properties. Diene polymers in particular tend to crosslinking and formation of gel particles when used in peroxidic processes. This tendency is enhanced by the inventive presence of vinyl end groups in the base polymers. The silane-grafted polymers have very low failure temperatures of only >43° C. (PAFT) or >60° C. (SAFT). The use of polyolefins with a high ethylene content inevitably means the presence of long ethylene blocks in the polymer. This in turn leads to poor wetting and adhesive properties on many plastics surfaces, such that very many adhesion problems cannot be solved in an optimal manner. In addition, long polyethylene sequences tend to peroxidic crosslinking (which is exploited industrially in the production of cable sheathing among other applications), as a result of which gel formation is unavoidable. The ungrafted base polymers have a relatively low molar mass and melt viscosity of not more than 50 000 cP at 177° C. The molar mass (and hence also the melt viscosity) is known to be degraded by chain cleavage in a peroxidically induced graft reaction. Corresponding polymers with high functionalization rates therefore inevitably have very low molar masses/melt viscosities, and are unsuitable for many application sectors. The use of relatively low molecular weight base polymers generally leads to rather low functionalization rates. Likewise described are resin compositions which already contain crosslinked poly(ethylene-co-1-olefin) polymers. Compositions containing such rubber-like constituents are unsuitable for visually demanding applications (poor surface structure) and also cannot be processed on many application systems customary in the adhesives section (for example melt spraying) (blockage of the application nozzles). The melt-applied adhesives described as the application have principally low melt viscosities. Likewise described is the use of crystalline and semicrystalline poly(propylene-co-1-olefin) polymers which are likewise said to be suitable for grafting. These have a propylene content of at least 50 mol % and preferably likewise a melt viscosity of not more than 50 000 cP at 177° C. (before grafting and after grafting), and a polydispersity of 1 to 5. Examples of poly(propylene-co-1-olefin) polymers include polymers of the VISTAMAXX, LICOCENE, Eastoflex, REXTAC and VESTOPLAST product series. Semicrystalline polyolefin polymers with a specific microstructure are not described. The crystallinity of the poly(propylene-co-1-olefin) copolymers is reported as 2-60% (i.e. 3-100 J/g), and is thus essentially in the range of high crystallinity. This in turn causes poor wetting of and/or poor adhesion to polyolefin surfaces, and rules out numerous fields of application.
EP0827994 describes the use of silane-grafted amorphous poly(alpha-olefins) as a moisture-crosslinking adhesive raw material or adhesive. The base polymers used are atactic polypropylene (aPP), atactic poly(1-butene), or preferably co- or terpolymers formed from C4-C10 alpha-olefins (0-95% by mass), propene (5-100% by mass) and ethylene (0-20% by mass). The silane-modified APAO described in the examples has a softening point of 98° C., a needle penetration of 15*0.1 mm and a melt viscosity of 6000 mPa*s. The atactic polyolefins and APAOs used have a relatively low molar mass and a relatively low crystallinity, which leads on modification to products with low flexibility, which possess a low functionality and a low tensile strength, and are therefore unsuitable for many applications.
The use of metallocene compounds as a catalyst in olefin polymerization has likewise been known for some time. Kaminsky et al. have shown that the cyclopentadienylzirconium dichloride/methylaluminoxane (Cp2ZrCl2/MAO) catalyst system is very suitable for polymerization (Adv. Organomet. Chem. 1980, 18, 99-149). Since this time, the use of metallocene compounds in conjunction with methylaluminoxane (MAO) has become widespread in polymerization reactions. For instance, there is a multitude of publications concerned with metallocene-catalysed olefin polymerization, for example of propene, for example U.S. Pat. No. 6,121,377, EP 584 609, EP 516 018, WO 2000/037514, WO 2001/46274 and US 2004/0110910.
In the polymerization of propene or higher homologues thereof, different relative stereoisomers may be formed. The regularity with which the configurative repeat units follow one another in the main chain of a macromolecule is referred to as tacticity. To determine the tacticity, the monomer units of a polymer chain are considered and the relative configuration of each (pseudo)asymmetric chain atom relative to the preceding atom is determined. Isotacticity refers to the situation where the relative configuration of all (pseudo)asymmetric chain atoms found is always the same, i.e. the chain is formed from only one single configurative repeat unit. Syndiotacticity, in contrast, refers to the situation where the relative configurations of successive (pseudo)asymmetric chain atoms are the opposite of one another, i.e. the chain is formed from two different alternating configurative repeat units. In atactic polymers, finally, the different configurative repeat units are arranged randomly along the chain.
The physical properties of propylene polymers depend primarily on the structure of the macromolecules and hence also on the crystallinity, the molecular weight thereof and the molecular weight distribution, and can be influenced by the polymerization process used and especially the polymerization catalyst used [R. Vieweg, A. Schley, A. Schwarz (eds.); Kunststoff Handbuch [Plastics Handbook]; vol. IV/“Polyolefine” [Polyolefins]; C. Hanser Verlag, Munich 1969].
Polypropylene polymers are thus divided into atactic, isotactic and syndiotactic polymers on the basis of their tacticity. Additional special forms include the so-called hemiisotactic polypropylene polymers and the so-called stereoblock polymers. The latter are usually polymers with isotactic and atactic stereoblocks which behave like thermoplastic elastomers, since a physical crosslinking of the polymer chains takes place, which leads to a connection of different crystalline polymer regions (A. F. Mason, G. W. Coates in: “Macromolecular Engineering”; Wiley-VCH, Weinheim; 2007).
Atactic polypropylene has a low softening point, a low density and a good solubility in organic solvents. Conventional atactic polypropylene (aPP) features a very wide molecular weight distribution, which firstly leads to a broad melting range, and secondly entails high low molecular weight fractions which have a greater or lesser tendency to migrate. aPP has a very low tensile strength of approx. 1 MPa, but on the other hand has a very high elongation at break of up to 2000% (H.-G. Elias; Makromoleküle; vol. III; Wiley-VCH; Weinheim; 2001). Owing to the low softening point, the thermal stability of aPP formulations is correspondingly low, which leads to a significant limitation in the area of use. Purely atactic polypropylene polymers can also be prepared by metallocene catalysis to obtain either very low molecular weight or relatively high molecular weight polymers (L. Resconi in: “Metallocene based Polyolefins”; J. Scheirs, W. Kaminsky (eds.); J. Wiley & Sons; Weinheim; 1999).
Syndiotactic polypropylene is highly transparent and is notable for good thermal stability, the melting temperature being below that of isotactic polypropylene. It has high fracture resistances coupled with moderate elongation at break (A. F. Mason, G. W. Coates in “Macromolecular Engineering”; Wiley-VCH, Weinheim; 2007). A disadvantage is the slow crystallization from the melt which is observed in many cases. Owing to physical loops, the melt viscosity of syndiotactic polypropylene with comparable molar mass is significantly higher than that of isotactic polypropylene, i.e. it is possible to achieve the same melt viscosity with significantly lower molar masses. Syndiotactic and isotactic polypropylene are immiscible from a certain molar mass; corresponding polymer blends tend to phase separation. Polymer blends of syndiotactic polypropylene with other polyolefins exhibit a significantly higher elongation at break than blends comprising isotactic polypropylene (T. Shiomura, N. Uchikawa, T. Asanuma, R. Sugimoto, I. Fujio, S. Kimura, S. Harima, M. Akiyama, M. Kohno, N. Inoue in: “Metallocene based Polyolefins”; J. Scheirs, W. Kaminsky (eds.); J. Wiley & Sons; Weinheim; 1999). Conventional heterogeneous Ziegler-Natta catalysts are incapable of preparing syndiotactic polypropylene.
Isotactic polypropylene features a high melting temperature and good tensile strength. For 100% isotactic polypropylene, the calculated melting temperature is 185° C. and the melting enthalpy is approx. 207 J/g (J. Bicerano; J. M. S.; Rev. Macromol. Chem. Phys.; C38 (1998); 391ff). As a homopolymer, however, it has a relatively low cold stability and a high brittleness, and a poor heatsealability or weldability. The tensile strength (fracture) is approx. 30 MPa, and virtually no elongation at break occurs. Improved material properties can be established by co- or terpolymerization with ethylene and 1-butene, the comonomer content for copolymers with ethylene being typically <8% by mass and, for terpolymers with ethylene and 1-butene, <12% by mass (H.-G. Elias; Makromoleküle; vol. III; Wiley-VCH; Weinheim; 2001). At the same MFR (melt flow rate), isotactic polypropylene which has been prepared by conventional heterogeneous Ziegler-Natta catalysis has a significantly lower intrinsic viscosity than polypropylene which has been prepared by metallocene catalysis. The impact resistance of the metallocene-based polymer is above that of the Ziegler-Natta material within a wide molar mass range (W. Spaleck in: “Metallocene based Polyolefins”; J. Scheirs, W. Kaminsky (eds.); J. Wiley & Sons; Weinheim; 1999).
Since the solubility of polypropylene depends both on the molecular weight and on its crystallinity, a corresponding fractionation can be effected by means of dissolution tests [A. Lehtinen; Macromol. Chem. Phys.; 195(1994); 1539ff].
With regard to the solubility of polypropylene polymers in aromatic solvents and/or ethers, there are numerous publications in the scientific literature. For example, it has been found that the proportion of xylene-soluble constituents is significantly <1% by mass for isotactic poly(propylene) homopolymer which has been obtained by metallocene catalysis; in the case of random copolymers with ethylene, according to the ethylene content, xylene-soluble fractions of not more than 5% by mass are found (W. Spaleck in: “Metallocene based Polyolefins”; J. Scheirs, W. Kaminsky (eds.); J. Wiley & Sons; Weinheim; 1999).
It has been known for some time that it is possible by means of extraction with ethers to obtain amorphous atactic fractions [J. Boor; “Ziegler-Natta Catalysts and Polymerization”; Academic Press; New York; 1979] and low molecular weight fractions with low crystallinity [G. Natta, I. Pasquon, A. Zambelli, G. Gatti; Makromol. Chem.; 70 (1964); 191ff] from polypropylene polymers. Highly crystalline isotactic polymers, in contrast, have a very low solubility both in aliphatic solvents and in ethers, specifically also at elevated temperature [B. A. Krentsel, Y. V. Kissin, V. I. Kleiner, L. L. Stotskaya; “Polymers and Copolymers of higher 1-Olefins”; p. 19/20; Hanser Publ.; Munich; 1997]. The soluble polymer fractions generally have only a very low crystallinity, if any, and do not exhibit a melting point [Y. V. Kissin; “Isospecific polymerization of olefins”; Springer Verlag; New York; 1985]. Tetrahydrofuran-soluble polypropylene oligomers have very low number-average molar masses of significantly less than 1500 g/mol [H. El Mansouri, N. Yagoubi, D. Scholler, A. Feigenbaum, D. Ferrier; J. Appl. Polym. Sci.; 71 (1999); 371ff].
The different polymer types differ significantly in their material properties. The crystallinity of highly isotactic or syndiotactic polymers is very high owing to their high order. Atactic polymers, in contrast, have a high amorphous content and accordingly a low crystallinity. Polymers with high crystallinity exhibit many material properties which are undesired especially in the field of hotmelt adhesives. For example, a high crystallinity in low molecular weight polymers leads to very rapid crystallization with open times (“open time”=time interval within which the parts to be adhesive bonded can be bonded to one another) of in some cases less than one second. In the case of application (for example in the case of nozzle application by spraying), this leads to blockage of the application equipment used even in the event of very small temperature variations, and hence to very poor process stability. An additional factor is the exceptionally short time interval within which the adhesive bond can be joined after the application. Highly crystalline polymers at room temperature are additionally hard and brittle and have only a very low flexibility, which is likewise undesired in the case of adhesive bonds. An additional factor is that very high amounts of energy are required for the melting of highly crystalline polymers at individual points (at the site of introduction) and over the entire conduit system, which, as well as economic effects, also has adverse effects for processability. Furthermore, in the case of highly crystalline polymers, there is spontaneous (immediate) solidification below the melting point (which, in analysis by means of differential calorimetry (DSC), is characterized by a sharp melting peak in the 2nd heating), which makes impossible or greatly complicates the processability of such polymers or of the products produced on the basis of such polymers.
The preparation of poly-1-olefins with isotactic propylene segments by use of metallocene catalysts is known.
For example, EP0384264 describes substituted and unsubstituted bisindenylzirconocenes with highly varying bridging elements for the preparation of polypropylene waxes with a propylene content of 80 to 99.75% by mass. Owing to their high crystallinity, their hardness and the poor adhesive performance in formulations, the isotactic crystalline waxes described are unsuitable for the uses intended in the present application. Modification using free-radical graft polymerization leads, owing to the unfavourable chain topology, to very significant polymer degradation with simultaneously low graft rates.
EP480390 describes a process for preparing polyolefins with high tacticity and high molar mass, in which the selection of a specifically adjusted system composed of metallocene catalyst and cocatalyst allows the use of aromatic solvents to be dispensed with. According to the examples, both isotactic and syndiotactic polymers are obtained, the isotacticity index of which is in the range from 90 to 99%, and the syndiotacticity index of which is 96%. Polymers with high proportions of atactic triads and polymers with a specific ratio of syndiotactic to isotactic and atactic structural elements are not described. Modification of the polymers described using free-radical graft polymerization likewise leads, owing to the unfavourable chain topology, to very significant polymer degradation at simultaneously low graft rates.
EP584609 describes rac/meso mixtures of substituted and unsubstituted bisindenyizirconocenes, with which it is possible to prepare mixtures of atactic and isotactic polyolefins. Meso forms of metallocene catalysts are known to prepare polymers with irregular undefined stereostructure, with simultaneously very low catalyst activities and poor reproducibility of the polymerization results. The use of such products in a free-radical graft polymerization leads to materials with poor material properties, especially in respect of material cohesion.
EP1263815 discloses substantially amorphous polymers based on poly(1-olefin) copolymers, which, owing to their rheological behaviour, are said to be suitable as adhesives, and a process for preparation thereof. As has long been known, amorphous polymers, however, have very unbalanced material behaviour. More particularly, the cohesion of such polymers is distinctly underdeveloped in relation to adhesion, and there is therefore frequently cohesive failure of adhesion in the corresponding adhesive bonds.
WO 01/46278 describes 1-olefin copolymers with predominantly amorphous character, which are obtained by metallocene catalysis. The use thereof as melt-applied adhesive is said to require only minimal additions of adhesive resins, if any. The copolymers consist of A: 60 to 94% of a C3-C6 1-olefin, B: 6-40 mol % of one or more C4-C10 1-olefins and optionally C: 0-10 mol % of another unsaturated monomer (preferably ethylene). The random distribution of the comonomer B disrupts the crystallinity of the polymers to a particularly high degree, since only few regions attain the minimum block length needed for crystallization (see, for example, S. Davison, G. L. Taylor; Br. Polym. J.; 4 (1972); 65ff). This is also evident, inter alia, from the low melting point of the polymers described. Substantially amorphous polymers additionally have very unbalanced material behaviour. More particularly, the cohesion of such polymers is distinctly underdeveloped in relation to adhesion, and there is therefore frequently a cohesive failure of adhesion in the corresponding adhesive bonds. Such polymers with a low melting point also lead to poor heat resistance in bonds, which rules out numerous fields of use. Comonomers with more than four carbon atoms are additionally very expensive, which makes the products uneconomic with regard to the fields of use thereof and the product prices to be achieved there. Freedom from aromatics is difficult to guarantee via the preparation process described, especially since preference is given to polymerizing in aromatic solvents, and the cocatalyst used does not dissolve in aliphatic solvents. The high reaction temperatures, which are above (in some cases very far above) the melting points of the polymers prepared, lead to very high reaction pressures which make it difficult to operate the polymerization process economically. An additional factor is that many inventive monomers are in the supercritical state in large parts of the process window specified (TR 40-250° C., pR 10-3000 bar), which requires a high level of technical complexity to control the process, and further limits the economic viability of the process.
Highly isotactic or syndiotactic polypropylene homo- or copolymers with ethylene and/or higher olefins, as described in the publications cited, are unsuitable for use as a melt-applied adhesive or adhesive raw material.
There was therefore a need for functionalized polyolefins with improved material properties, especially in functionalized polyolefins which are prepared on the basis of unfunctionalized polyolefins with a defined polymer structure, which enable a high degree of functionalization with simultaneously moderate polymer degradation owing to their defined chain structure in the free-radical functionalization. At the same time, the functionalized polyolefins should additionally exhibit highly cohesive material behaviour coupled with good adhesive properties, without having the disadvantages of highly crystalline polymer systems.